This invention relates to liquid phase epitaxial growth of crystalline semiconductor material and more particularly to a method for growing extremely smooth layers of semiconductor material.
In multi-layered semiconductor devices, it may be desirable to grow extremely thin (less than 1 .mu.m) layers. In these cases, the interfaces between the layers must be extremely smooth since even a small amount of roughness will often adversely effect the performance of the device. For example, the structure of a GaAs injection laser, designed for continuous operation at room temperature, has a recombination region which is typically 0.2 .mu.m thick. An interface roughness of even 0.05 .mu.m in this device would constitute a 25 percent variation in thickness and would decrease the device performance considerably. Therefore, it is necessary, when growing extremely thin layers of semiconductor material, that the surfaces and hence the interfaces be as smooth as possible.
Present liquid phase epitaxy techniques do not yield sufficiently smooth surfaces on thin layers. When both the substrate and the liquid phase solution are maintained at the same temperature during the crystal growth, the layer's surface has an intolerable degree of roughness. It is also well known, that layers may be grown in liquid phase epitaxy by keeping the solution a few degrees warmer than the substrate. Heretofore, with this latter technique, the temperature difference was at least 1.degree. C. This difference in temperature is too great to produce a sufficiently smooth surface on layers which are less than 1 .mu.m thick.